A plumb-bob or a plummet is a weight with a pointed tip on the bottom that is suspended from a string and used as a vertical reference line.

This instrument has been used since the time of the ancient Egyptians by bricklayers, masons, and carpenters to ensure that their constructions are "plumb", or perfectly upright. It may also be used in surveying to sight a point on the ground that is not readily visible. Small plumb bobs are included in the kits of various instruments such as levels and theodolites. They are used to set the instrument exactly over a fixed datum marker, prior to taking fresh readings.Fact|date=May 2008

Etymology of the name

The "plumb" in the name "plumb-bob" comes from the fact that such tools were archetypically made of lead (Latin ""). The adjective "plumb" developed by extension.


Up until the modern age, on most tall structures, plumb-bobs were used to provide vertical datum lines for the building measurements. A section of the scaffolding would hold a plumb line that was centered over a datum mark on the floor. As the building proceeded upwards the plumb line would also be taken higher, still centered on the datum. Many cathedral spires, domes and towers still have brass datum marks inlaid into their floors, that signify the center of the structure above.Fact|date=May 2008

The early skyscrapers used heavy plumb-bobs hung on wire in their lift wells. The weight would hang in a container of oil to dampen any swinging movement, functioning as a shock absorber.Fact|date=May 2008

Often, figure drawing students will also make use of a plumb line to find the vertical axis through the center of gravity of their subject and lay it down on paper as a point of reference. The device used may be purpose-made plumb lines, or simply makeshift devices made from a piece of string and a weighted object, such as a metal washer. This plumb line is important for lining up anatomical geometries and visualizing the subject's center of balance.Fact|date=May 2008


* [ 60 oz. Plumb Bob] .
* [ String Line and Plumb Bob] .

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Look at other dictionaries:

  • Plumb bob — Plumb Plumb (pl[u^]m), n. [F. plomb, L. plumbum lead, a leaden ball or bullet; cf. Gr. mo lybos, mo libos, mo lybdos. Cf. {Plummet}, {Plunge}.] A little mass or weight of lead, or the like, attached to a line, and used by builders, etc., to… …   The Collaborative International Dictionary of English

  • plumb bob — n. PLUMB (n.) …   English World dictionary

  • plumb bob — plumb′ bob n. bui sur plummet 1) • Etymology: 1825–35 …   From formal English to slang

  • plumb bob — noun the metal bob of a plumb line • Syn: ↑plumb, ↑plummet • Derivationally related forms: ↑plumb (for: ↑plumb) • Hypernyms: ↑bob …   Useful english dictionary

  • plumb-bob — /ˈplʌm bɒb/ (say plum bob) noun a piece of lead or some other weight attached to a line, used for determining perpendicularity, for sounding, etc.; the bob of a plumb line. Also, plummet …   Australian English dictionary

  • plumb bob — noun Date: circa 1840 the metal bob of a plumb line …   New Collegiate Dictionary

  • plumb bob — noun a bob of lead or other heavy material forming the weight of a plumb line …   English new terms dictionary

  • plumb bob — noun A metal weight attached to the end of a plumb line …   Wiktionary

  • plumb bob — plummet (def. 1). [1825 35] * * * …   Universalium

  • plumb-bob — …   Useful english dictionary